1. Field of the Invention
The present invention relates to a phase splitter and particularly to a phase splitter with active load and feedback tuning circuit.
2. Description of the Prior Art
FIG. 1 is a diagram showing a conventional phase splitter. It includes a transistor M, resistors Rd and Rc, and a capacitor Cc. The source of the transistor M is coupled to the resistor Rc. The drain of the transistor M is coupled to the resistor Rd. The gate of the transistor M is coupled to receive an input signal IN. The resistors Rc and Rd are also coupled to receive a power supply voltage Vss and Vdd respectively. The two ends of the capacitor Cc are respectively coupled to the source of the transistor M and to receive the voltage Vss. Output signals OUT1 and OUT2 are output from the drain and source of the transistor M respectively.
The phase difference of the output signals OUT1 and OUT2 is determined by the resistors Rc and Rd, and the capacitor Cc.
However, in the conventional phase splitter, a relatively large circuit area is needed due to the passive load and it is difficult to tune the phase difference between the output signals.
The object of the present invention is to provide a phase splitter with active load and feedback tuning circuit, which uses a small circuit area, generates a more precise and tunable phase difference.
The present invention provides a phase splitter comprising a transistor having a gate receiving an input signal, a drain and source outputting a first and second output signal with a first and second phase, respectively, a current source providing a current flowing from the drain to the source of the transistor, and a feedback tuning circuit receiving the first and second output signal, and tuning the current according to the first and second phase.
The present invention further provides a phase splitter comprising a first transistor of a first type having a gate receiving an input signal, a drain and source outputting a first and second output signal with a first and second phase, respectively, a second transistor of the first type having a drain coupledto the source of the first transistor and a source receiving a first voltage, a third transistor of the first type having a drain and gate commonly coupledto a gate of the second transistor, and a source receiving the first voltage, a fourth transistor of a second type having a drain and gate coupled together, and a source receiving a second voltage, a fifth transistor of the second type having a gate coupled to the gate of the fourth transistor, a source receiving the second voltage and a drain coupled to the drain of the first transistor, a resistor coupled between the drains of the third and fourth transistor, a capacitor having two ends respectively coupled to the gate of the second transistor and receiving the first voltage, and a feedback tuning circuit receiving the first and second output signal, and generating a third voltage to the gate of the second transistor corresponding to the first and second phase.
The present invention also provides a phase splitter comprising a first transistor of a first type having a gate receiving an input signal, a drain and source outputting a first and second output signal with a first and second phase, respectively, a second transistor of the first type having a drain coupled to the source of the first transistor and a source receiving a first voltage, a third transistor of the first type having a drain and gate commonly coupled to a gate of the second transistor, and a source receiving the first voltage, a fourth transistor of a second type having a drain and gate commonly coupled to the drain of the third transistor, and a source receiving a second voltage, a fifth transistor of the first type having a gate and drain coupled together, a source receiving the first voltage, a sixth transistor of the second type having a gate and drain commonly coupled to the drain of the fifth transistor, and a source receiving the second voltage, a seventh transistor of the second type having a source receiving the second voltage, a gate coupled to the gate of the sixth transistor and a drain coupled to the drain of the first transistor, a capacitor having two ends respectively coupled to the gate of the second transistor and receiving the first voltage, and a feedback tuning circuit receiving the first and second output signal, and generating a third voltage to the gate of the second transistor corresponding to the first and second phase.
Thus, in the present invention, a feedback loop is achieved by a phase tuning circuit and a current source is used as an active load. The phase tuning circuit feeds back a voltage controlling the current of the current source, whereby the phase difference is more precise and tunable.